The present invention relates to a water-repellent powder and to a method for the preparation thereof. More specifically, the present invention relates to a water-repellent powder comprising powder whose surface is coated with triorganosiloxysilicic acid and to a method for the preparation thereof.
Due to their excellent flowability, dispersibility, and lipophilicity, water-repellent powders are widely employed for cosmetics, pharmaceuticals, organic resins, paints, coatings, and magnetic material. Known water-repellent powders include, for example, water-repellent powders prepared by treating the surface of a powder with dimethyldichlorosilane (Japanese Patent Application Laid Open [Kokai or Unexamined] Number Sho 50-51494 [51,494/1975]), water-repellent powders prepared by treating the surface of a powder with hexamethyldisilazane (Japanese Patent Application Laid Open Numbers Sho 50-51494 and Sho 53-9297 [9,297/1978]), and water-repellent powders prepared by treating the surface of a powder with methylhydrogenpolysiloxane (Japanese Patent Publication [Kokoku] Number Hei 1-54381 [54,381/1989]).
However, the water-repellent powders disclosed in Japanese Patent Application Laid Open Numbers Sho 50-51494 and Sho 53-9297 contain residual hydrogen chloride or ammonia (reaction by-products), and this places limitations on the application of these water-repellent powder products in cosmetics, and organic resins. The water-repellent powder disclosed in Japanese Patent Publication Number Hei 1-54381 evolves hydrogen during its storage, which raises the risk of explosion during the storage of this type of powder. Moreover, when this water-repellent powder is employed in cosmetics, it can cause such problems as a change in the color of the cosmetic, foundation caking, tarnishing mirrors positioned over the foundation. When the water-repellent powder disclosed in Japanese Patent Publication Number Hei 1-54381 is employed in organic resins, it evolves hydrogen gas when the organic resin is molded and/or with the simple passage of time. This causes the appearance of bubbles in the organic resin, with a resulting substantial decline in the strength of the organic resin. Finally, the use of this type of water-repellent powder in inks is associated with a strong tendency for the ink pigment to aggregate.
The preparative methods for the water-repellent powders disclosed in the aforementioned patents require the careful removal of reaction by-products that are released during the manufacturing process, e.g., hydrogen chloride, ammonia, or hydrogen, and this requirement results in each case in a poor productivity.